In July of this year, 89 dolphins were found stranded on the shore between North Carolina and New York; by the first week in October, the death toll rose to 553 and that number continues a steep climb. Although scientists suspect a virus, they have recently begun to shift the blame: humans may be a large part of the reason why so many dolphins are dying.

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"It all comes back to the wider impacts our collective activities and effluent are having on the coastal marine environment," Courtney Vail, the Campaigns and Programs Manager for Whale and Dolphin Conservation (WDC), told Digital Journal. "The byproducts of our industrial society are taking a toll on marine life, including compromised immune systems in dolphins and other marine mammals that bioaccumulate toxins." In other words, a virus is killing the dolphins, but they probably would never have gotten sick if it weren't for us.

'Unusual Mortality Event' with a Usual Cause

Scientists believe the high number of dolphins washing ashore to constitute an "unusual mortality event" as the National Oceanic and Atmospheric Administration has dubbed it. The response to this catastrophe is an emergency investigation and analysis of dolphin remains. As reported in National Geographic, each dolphin corpse is taken into the lab for evaluation in order to see whether any visible indications suggest a cause of death. Next, scientists take and test tissue samples for viruses. After that, they assess the blubber and organs, including the kidneys, for traces of heavy metals.

After considerable effort, suspicions and consensus have focused on the familiar morbillivirus, an infection similar to that which causes measles in humans, distemper in dogs, and rinderpest in cattle, according to Scientific American.More than 700 dolphins died over a ten month span during 1987 and 1988 due to this very same virus. The virus cannot be prevented by artificial measures such as inoculation, though over time surviving dolphins will pass on a natural immunity to their offspring. This year, Scientific American noted, researchers believe coastal dolphins caught the virus from offshore populations; as viruses continually mutate, the dissemination of the virus through the dolphin tribe occurred more or less naturally and resulted in the high mortality rate during the past few months. (Consider, for a moment, that many ailing dolphins die at sea, so the dead bodies that become stranded on shore represent only a percentage of the total death count.)

Because the ocean is an ecosystem, this dolphin event may be indicative of a wider problem, namely, that oceanic life is gradually becoming sickened due to human activity. "Dolphins are some of the most toxic animals on the planet, and it makes their immune system compromised because they're carrying so many heavy metals and toxins that accumulate in the food web," Matthew Huelsenbeck, a marine scientist at the nonprofit Oceana, told National Geographic.

Experts from the National Marine Fisheries Service estimate that roughly 20,000 dolphins live in coastal waters, while more than 81,000 occupy the deep waters off the continental shelf. How many more are fated for death this year?